The present invention relates to the field of implantable medical devices. More particularly, the present invention relates to cardiac pacing systems that provide a method for gradually increasing a pacing function from an initial value to a target pacing function value in an implantable medical device.
Implantable pulse generators (IPGs or pacemakers) with rate control are well known in the art. Rate control is usually accomplished using one or more rate responsive sensors to sense a parameter such indicative of the level of patient activity such as Q-T interval, exercise and the like. On the basis of the sensed parameter a desired pacing rate is set so that the cardiac demand of the patient may be met. Accordingly, such pacemakers typically employ algorithms to convert sensed parameters into a pacing rate such that a sensed increase in patient activity results in a higher pacing rate.
Certain IPGs may also be programmed with data relating to pacing rate. For example, values for a lower pacing rate limit and for an upper pacing rate limit may be programmed into an IPG. Such IPGs are typically referred to in the art as xe2x80x9crate responsive IPGsxe2x80x9d, and may have a variable pacing rate which changes depending on cardiac conditions such the cardiac workload of a patient. Initial parameter settings for such rate responsive IPGs are often based on clinical experience in combination with patient specific parameters such as age, lifestyle, health and so on.
Some IPG functions may be set to be automatically adjusted according to a patient""s changing needs. In some cases, and especially in patients who have had their rate responsive IPGs replaced, a xe2x80x9cFast Learnxe2x80x9d procedure may be employed where the patient performs a predetermined exercise and the results of the exercise are used to set IPG rate response parameter settings individualized to the patient""s particular needs and condition. Parameters for an IPG""s pacing rates may also be set subsequent to implantation, such as before the patient is dismissed from the hospital or during a follow up visit.
Increases in the pacing rate of the heart are often required in patients who receive IPGs. It is frequently desired to increase the heart rate of a patient suffering from bradycardia whose heart is beating at a rate that is too slow. In such cases, an IPG may be implanted to restore the patient""s heart rate to a normal level. It has been discovered, however, that an immediate increase in the pacing rate of a heart in a patient suffering from bradycardia can lead to problems such as patient discomfort. At least in the case of patients suffering from bradycardia, these problems have their roots in the fact that over a period of years a patient""s heart may have become accustomed to beating at a slow rate, and the heart does not respond well to suddenly being forced to beat at a higher rate.
Thus, a need exists in the medical arts for adjusting the pacing of a patient""s heart in a gradual or incremental manner so that a pacing rate may be increased gradually to a target value.
Some methods have been proposed in the prior art for gradually adjusting the pacing rate of a heart. For example, U.S. Pat. No. 5,944,743 to Janssens discloses a pacemaker system for enabling special rate control for patients who have specially recognized conditions, such as patients who have undergone cardiac ablation procedures and who are particularly susceptible to bradycardia-dependent ventricular fibrillation or other arrhythmias. In such patients, the heart is typically paced at a high start value and brought down to a predetermined lower rate limit. The most pertinent prior art patent known of the present time is shown in the following table:
The patent listed in Table 1 is hereby incorporated by reference herein in its entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, at least some of the devices and methods disclosed in the patent of Table 1 may be modified advantageously in accordance with the teachings of the present invention.
The present invention is therefore directed to providing a method and system for gradually increasing the rate at which pacing pulses are delivered to a patient""s heart after the patient has received an IPG. The system of the present invention overcomes at least some of the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of gradually increasing the rate at which a heart is paced in a cardiac pacing system.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the pacing of cardiac tissue. Those problems include, without limitation: (a) patients experiencing discomfort after undergoing an implant procedure where an IPG is implanted to remedy slow heart rates; (b) patients"" hearts suddenly being forced by implantable cardiac stimulators to beat at rates which are excessive; (c) applying initial pacing rates to patients which are uncomfortably high or excessive; (d) difficulty in determining an appropriate initial pacing rate for a particular patient, and (e) difficulty in determining a final target pacing rate for a particular patient.
In comparison to known pacing techniques, various embodiments of the present invention provide one or more of the following advantages: (a) increasing patient comfort following a pacemaker implant; (b) xe2x80x9ctrainingxe2x80x9d the heart in an optimal fashion after a pacemaker implant so that the heart becomes accustomed to beating at rates higher than those attained prior to the implant, and (c) fewer patient complaints or returns to hospital following the implant of an IPG.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of providing electrical stimuli to a patient""s cardiac tissue at a rate which is time-dependent such that the average or mean rate at which pacing stimuli are applied to cardiac tissue increases gradually over a predetermined training period; (a) methods corresponding to (a) of applying such gradually increasing pacing rates to a heart following an IPG implant; (c) methods corresponding to (a) of operating an IPG to permit an initial value of a pacing rate to be determined, permitting a target value of a pacing rate to be determined, and permitting a target pacing value to be attained by a training increment during a training period.
At least some embodiments of the present invention involve determining an initial value of a pacing rate. A target value of the pacing rate is then determined. The initial value of the pacing rate is increased to the target value by a training increment during a training period. Cardiac tissue may be paced initially at a rate determined by the initial value of the pacing rate. The length of the training period may be varied according to the desires of the attending physician, in response to the detection of certain conditions, or in response to the fulfillment of predetermined criteria. A calculated value of the pacing rate function may then be determined based on a determined training increment. The cardiac tissue may be paced at the initial calculated value of the pacing rate, and the pacing rate increased according to the determined training increment.